Hundreds of thousands of people marched for hours in searing heat on Sunday to express their frustration with how Hong Kong is run, in the latest phase of a crisis of governance in the former British colony.

Whistles, drums, horns and loud chanting went on into the night as a determined core of demonstrators marched on the 15th anniversary of the handover of Hong Kong from British to Chinese rule.

Though an annual event, Sunday's demonstration was the largest since that of 2003, which helped bring down the first Beijing-backed chief executive, Tung Chee-hwa. Organisers estimated that 400,000 people were on the march.

Throughout the day, protesters including young families, students and politicians surged out of Victoria Park into cordoned-off streets lined by police, towards the central government offices.

In the morning, a new chief executive, Leung Chun-ying, was sworn in by the visiting Chinese president, Hu Jintao, in a scrupulously controlled ceremony. Even there, a lone protester managed to shout out demands for China to account for the deaths of hundreds around Tiananmen Square in Beijing on 4 June 1989, before he was quickly hustled out of sight.

Hu expressed China's confidence in Hong Kong's role as a free, law-abiding society, though in a sign of Beijing's anxiety over recent tensions, he appealed for unity. "While we recognise Hong Kong's achievements 15 years after the handover, we must also be conscious of the deep disagreements and problems in Hong Kong society," Hu said.

But there were demands from the streets for more representative government to replace a system in which Leung, a self-made millionaire, was chosen by 689 members of a 1,200-member hand-picked committee largely owing allegiance to Beijing.

Anger at the perceived manipulation of what was promised to be "Hong Kong people running Hong Kong" has been joined in recent weeks by disgust at reports of outgoing leader Donald Tsang revelling in a lifestyle including tycoons' private jets, lavish hotels and a sweetheart luxury property offer, since rejected.

Alongside the local political demands for democracy, many demonstrators highlighted human rights concerns, with some carrying pictures of the detained blind and deaf Chinese dissident Li Wangyang, who was found hanged with his feet still touching the floor in what Chinese officials have chosen to describe as a suicide.

Fear of China has meshed with a generalised contempt for the incoming leader. Leung, 57, known widely as CY. Banners ranged from the pithy "F.U.C.Y." to pictures of the property surveyor millionaire with the long nose of Pinocchio.

A surprise winner against Henry Tang in the March process to select a new leader, CY is seen by many as too close to Beijing.

"We don't like CY" said a retired teacher KY Tsang, when asked why he and his wife had decided to join the demonstration for the first time. "We don't like to see the intervention of China into our affairs."

His wife added that she did not think one demonstration could change things, "but we hope we can slow down their aggression".

"And I mean the terrible torture of pro-democracy people such as Li Wangyang. It is unacceptable, unbelievable. Such a crime could only happen in a totalitarian country," she said, choosing not to give her name.

A statement from Leung's new administration insisted his government would uphold the "core values" of Hong Kong – a catchphrase intended to cover freedom of expression and assembly and the rule of law.

"I am here to express my view that there is a lot of unfairness here," said Abel Lau, a younger teacher. "The first thing is that freedom of speech is not as free as before. And the government is not doing so well – it is leaning towards corporate and business persons. They don't represent us, but they have the power," he said.

Recent surveys have shown higher numbers than ever before of people choosing to identify themselves as Hong Kong people instead of as Chinese.

More prevalent than in previous years were people waving the Hong Kong colonial flag, a combination of the UK union flag with the pre-1997 Hong Kong coat of arms.